Beam-driven Plasma Acceleration: Critical Issues on the Road to a Collider

1. Beam-driven Plasma Acceleration:Critical Issues on the Road to a Collider Tom Katsouleas Professor and Dean, Duke Pratt School of Engineering Advanced Accelerator Concepts Workshop July 28, 2008

2. Collaborators

3. Outline • Brief History • Physical pictures and comparisons • Starting point of path – current results @SLAC, ATF • Path to a high energy collider • Critical issues, milestones, prospects

4. ILC Current Energy Frontier E164X/E-167 LBL RAL LBL Osaka UCLA ANL Plasma Accelerators -- Brief History • 1979 Tajima & Dawson Paper • 1981 Tigner Panel rec’d investment in adv. acc. • 1985 Malibu, GV/m unloaded beat wave fields, world-wide effort begins • 1988 ANL maps beam wakes • 1992 1st e- at UCLA beat wave • 1994 ‘Jet age’ begins (100 MeV in laser-driven gas jet at RAL) • 2004 ‘Dawn of Compact Accelerators’ (monoenergetic beams at LBNL, LOA, RAL) • 2007 Energy Doubling at SLAC

5. Research program has put Beam Physics at the Forefront of Science Acceleration, Radiation Sources, Refraction, Medical Applications

6. From Science to a ColliderRequirements for High Energy Physics • High Energy • High Luminosity (event rate) • L=frepN2/4psxsy • High Beam Power • ~20 MW • High Beam Quality • Energy spread dg/g ~ .1 - 10% • Low emittance: en ~ gsyqy << 1 mm-mrad • Reasonable Cost • Gradients > 100 MeV/m • Efficiency > few %

7. Linear Plasma Wakefield Theory Large wake for a laser amplitude ao=eEo/mwoc ~ 1 or a beam density nb~ no For ctpulse of order cpwp-1 ~ 30m (1017/no)1/2 and spot sizes=c/wp ~ 15m (1017/no)1/2 : • P ~ 15 TW (tpulse/100fs)2 laser • Q/ tpulse = 1nCoul/100fs (I~10 kA) beam Beam Requirements on I, t, s, g require a Multi-GeV-class facility Ultra-high gradient regime and long propagation issues not possible to access with a 50 MeV beam facility

8. Beams vs. Lasers?(I. Physics) • Wakes and Beam Loading are Similar • - minor differences in transverse profiles • Driver propagation and coupling efficiency – • - Beams more easily propagate over meter scales (no channel needed) • LR ~ ps2/l ~ ps2/1m vs b* ~ ps2/en ~ gps2/1m • - Beams have fundamentally higher coupling efficiency to wake (~ 2X) • lasers can distort due to dispersion, photon deceleration • 25 GeV and 2 GeV beam nearly identical • 55% beam to wake coupling achieved in E-167

9. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + - - - - - - - - - drive beam + - - + + + + + - + + + + + - + + + + + + + - - - - + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + - - - - - - + + + + + + + + + + + + - - - - - - - + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - + + + + + + + + - - - - - - - - - Ez Nonlinear Wakefield Accelerators (Blowout Regime) Rosenzweig et al. 1990 • Plasma ion channel exerts restoring force => space charge oscillations • Linear focusing force on beams (F/r=2pne2/m) • Synchrotron radiation • Scattering • Nonlinear Theory : W. Lu et al., PRL 16, 16500 [2006]

10. Limits to Energy Gain • Beam propagation • Head erosion (L=ps2/e) • Hosing • Transformer Ratio: E- load driver E+

11. On ultra-fast timescales, relativistic plasmas can be robust, stable and disposable accelerating structures Accelerator Comparison • No aperture, BBU • Instead tolerances of aligning witness, driver TESLA structure l ~ 30cm 2a Plasma l ~ 100mm

12. Path to a collider builds on recent success • Energy Doubling of 42 Billion Volt Electrons Using an 85 cm Long Plasma Wakefield Accelerator 42 GeV 85GeV Nature v 445,p741 (2007)

13. And builds on advances in diagnostics, simulations and physics understanding Focusing & Matching e- Halo Formation &εGrowth e+ Accepted for publication Phys. Rev. Lett. 2008 Page

14. Two Bunch Experiments at ATF Patric Muggli, Efthymios Kallos USC, Los Angeles, California Marcus Babzien, Karl Kusche, Vitaly Yakimenko Brookhaven National Laboratory, Upton, Long Island, NY Wayne D. Kimura, STI Optronics, Inc., Bellevue, WA Work supported by US DoE. Thank you! 14 P. Muggli, AAC 08 07/29/08

15. 2 Bunch Experimental Layout x E • 2 Bunches in energy • 2 Bunches in time? Figure by W.Kimura Next: In time

16. Witness Bunch Energy Gain (5mm plasma) 200 MeV/m acceleration of witness E. Kallos et al., Phys. Rev. Lett. 2008

17. A Mask Techniquefor the Generationof Trains of Microbuncheswith SubpicosecondSpacing and Length Patric Muggli, Efthymios Kallos USC, Los Angeles, California Marcus Babzien, Karl Kusche, Vitaly Yakimenko Brookhaven National Laboratory, Upton, Long Island, NY Wayne D. Kimura, STI Optronics, Inc., Bellevue, WA Work supported by US DoE. Thank you! 17 P. Muggli, AAC 08 07/29/08

18. To Plasma FEL, … Correlated energy chirp from linac Choose microbunches spacing and widths with mask and beam parameters: N, ∆z, z, Q Emittance selection (e- not absorbed, energy loss ≈3%) Multibunch Generation @ ATF “CPA system with filtering” Nguyen & Carlsten, NIM A 1996 18 P. Muggli, AAC 08 07/29/08

19. Equidistant Drive Bunches Witness Bunch To Plasma p p p= plasma wavelength Generate “ideal” spacing for resonant PWFA Charge modulation optimization possible Plasma density must be adjusted for resonant excitation TRAIN FOR PWFA Mask with non-equidistant “wires” Measurement in energy plane Energy 19 P. Muggli, AAC 08 07/29/08

20. Multi-bunch Afterburner Drivers: 75pC*(1:3:5:7)~1nC Witness: 0.3/R*1nC~50pC Transf. Ratio ~ 7 Transformer Efficiency ~ 30% Themos Kallos, USC

21. Path to a TeV Colliderfrom present state-of-the-art* • Starting point: 42 --> 85 GeV in 1m • Few % of particles • Beam load • 25 --> 50 GeV in ~ 1m • 2nd bunch with 33% of particles • Small energy spread • Preserve emittance • Replicate for positrons • Marry to high efficiency driver • Stage 20 times * I. Blumenfeld et al., Nature 445, 741 (2007)

23. First Self-consistent PWFA-LC Design FACET/BELLA Joint Review July 21 - 23, 2008

24. FACET/BELLA Joint Review July 21 - 23, 2008 FACET: Facility for Advanced Accelerator Experimental Tests • Use the SLAC injector complex and 2/3 of the SLAC linac to deliver electrons and positrons • Compressed 25 GeV beams  ~20 kA peak current • Small spots necessary for plasma acceleration studies • Two separate installations • Final bunch compression and focusing system in Sector 20 • Expanded Sector 10 bunch compressor for positrons

27. Nominal 25 GeV stage Preionized np= 11017cm-3 Ndriver = 2.91010, r= 3 m, z = 30 m, Energy = 25 GeV Ntrailing = 1.01010 , r= 3 m , z = 10 m, Energy = 25 GeV Spacing= 110 m Rtrans = -Eacc/Edec > 1 (Energy gain exceeds 25 GeV per stage) 1% Energy spread Efficiency from drive to trailing bunch ~48%!

28. Critical Issues Red=FACET only Blue=FACET Green=Facet partial

29. Positron Acceleration -- two possibilitiese- e+ or e+ e+ e- e+ e-/e+ e+/e+ e+ load • • Non-uniform focusing force (r,z) • Smaller accelerating force • Much smaller acceptance phase for acceleration and focusing Ref. S. Lee et al., Phys. Rev. E (2000); M. Zhou, PhD Thesis (2008), K. Lotov

31. Other Paths to a Plasma-based Collider • Hi R options --> 100 GeV to TeV c.m. in single stage • Ramped drive bunches or bunch trains • Plasma question: hose stability • RF Driver questions: pulse shaping techniques, drive charge is 5x larger • Or 10 GeV to TeV cm in 10 stages (increases gradient by x5) Ramped Driver w/ Gaussian Load • h>75% beam loading efficiency • 1% energy spread

32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Worldwide Experimental Effort on Plasma Accelerators Laser Wake Expts Electron Wake Expts e-/e+ hi g Wake Expts

33. WARNING • The following slides contain subjective material and may be offensive to some audiences. Parental discretion is advised. ACCEPT

34. Beams vs. Lasers?II. Wakes and beam loading are similar but… • Lasers can more easily reach the peak power requirements to access large amplitude plasma wakes • - $100k for a T3 laser vs $5M for even a 50 MeV beam facility • Average power cost for beam vs. laser technology sets timescale for HEP app • - $104/Watt for lasers currently x 200 MW ~ $20T driver developing, Barty talk • - $10/Watt for CLIC-type RF x 100 MW now

35. Summary • Recent success is very promising • No known show stoppers to extending plasma accelerators to the energy frontier • Many questions remain to be addressed for realizing a plasma-based collider • FACET-class facility is needed to address them • Lower energy beam facilities, laser facilities cannot access critical issues in the regime of interest now • FACET can address most issues of one stage of a multi-stage e-e+ TeV collider within 10 years

36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FACET is a Global Resource for the Field: Many Lasers – Only one SLAC Laser Wake Expts Electron Wake Expts e-/e+ hi g Wake Expts

37. Backup and Extra

38. Critical Issues follow from energy gain and beam quality considerations px x sx Uncompensated Nonlinear Focusing forces leads to Emittance growth after several betatron periods (effective area increased) • Energy Gain=eEloaded x Lacc • eEloaded= Gradient of Loaded wake • Wakefield amplitude (accelerating and focusing fields) • Beam loading • Lacc= acceleration length • LdephasingNot an issue for PWFA • LpumpdepletionTransformer Ratio • LdiffractionHead Erosion • LinstabilityHosing Plasma focusing causes beam to rotate in phase space Radially dependent accelerating field leads to energy spread

39. Driver to Plasma Coupling Efficiency • Laser -- Photon deceleration and dispersion alter pulse shape • Limits coupling efficiency • Beam – 25 GeV and 1 GeV beam have nearly identical shape (negligible phase slippage and distortion occurs) • Efficiency >95% possible • >55% achieved in E-167

40. Original beam loading simulation results: 1987 Drive beam (laser or particle beam) Note that wedge gives nearly constant decelerating field Properly phased trailing beam of particles: Loads wake • In linear theory just use superposition: • Add wakes => (for spot size c/wp) • 100% energy extraction (though Vgr=0) • 100% energy spread Katsouleas, Wilks et al., 1987

41. U C L A PIC Simulations of beam loading nonlinear regime flattens wake, reduces energy spread Beam load Ez Unloaded wake • Loaded wake • Nload~30% Nmax (h>75%) • 1% energy spread

42. Emittance Preservation px x s Several betatron periods (effective area increased) 1/4 betatron period (tails from nonlinear Fp ) • Emittance en = phase space area: Plasma focusing causes beam to rotate in phase space • Matching: Plasma focusing (~2pnoe2s) = Thermal pressure (grad p~e2/s3) • No spot size oscillations (phase space rotations) • No emittance growth Fp Fth

43. Nonlinear physics is unavoidable for either PWFA or LWFAWhy? Beam density Beam load efficiency Matching Energy spread=> bunch length Gives For typical collider parameters

44. How does this change if we restrict to linear wakes? For linear beam loading N < 106 Incompatible with high luminosity and efficiency

45. Ion Motion • Ion motion when • Matched beam spot size shrinks at large g, low en • For future collider • eny down by 102 (e.g., 10nm-rad) • g up by 10+ • nb up by 102 • Ion motion must be included in design/models Density wake of m-scale beams Ref. S. Lee et al., AAC Proc (2000); J. Rosenzweig et al., PRL (2006)

46. R. Gholizadeh et al.

48. Hosing in the blow-out regime Huang et al., Phys. Rev. Lett. Phys. Rev. Lett. 99, 255001 (2007) Parameters: Ipeak = 7.7 kA

49. Experimental Data – Energy Loss E (MV/m) # Particles Plasma OFF W D 4x1015 cm-3 Plasma ON • -1.3MeV over 6mm  -200MeV/m (Witness)

50. Experimental Data – Energy Gain E (MV/m) # Particles Plasma OFF W D 1x1016 cm-3 Plasma ON • +0.9MeV over 6mm  +150MeV/m (Witness)